You can override the `mail\.track\.value`\ model\ and\ store\ the\ values\ in\ the\ `old_value_char`\ and\ `new_value_char`\ separated\ by\ a\ comma\.\ Works\ like\ a\ charm\ for\ tracking\ changes\ on\ tags\ for\ example\.

class\ MailTrackingValue\(models\.Model\):
\ \ \ \ _inherit\ =\ 'mail\.tracking\.value'

\ \ \ \ @api\.model
\ \ \ \ def\ create_tracking_values\(self,\ initial_value,\ new_value,\ col_name,\ col_info,\ tracking_sequence,\ model_name\):
\ \ \ \ \ \ \ \ values\ =\ super\(MailTrackingValue,\ self\)\.create_tracking_values\(initial_value,\ new_value,\ col_name,\ col_info,\ tracking_sequence,\ model_name\)
\ \ \ \ \ \ \ \ if\ not\ values\ and\ col_info\['type'\]\ ==\ 'many2many':
\ \ \ \ \ \ \ \ \ \ \ \ field\ =\ self\.env\['ir.model.fields']._get(model_name, col_name)
            if not field:
                return
            values = {
                'field': field.id,
                'field_desc': col_info['string'],
                'field_type': col_info['type'],
                'tracking_sequence': tracking_sequence,
                'old_value_char': ', '.join([r.name_get()[0][1] for r in initial_value]),
                'new_value_char': ', '.join([r.name_get()[0][1] for r in new_value]),
            }
        return values

Hi,

You can add track_visibility attribute to field's declaration and use 'always' or 'onchange' to track every changes of field.

Ex 
partner_id = fields.Many2one('res.partner',track_visibility='always')